Terry Barnes is a regular contributor to the Australian edition of The Spectator and a former senior ministerial adviser to Tony Abbott.

Observing British politics from the far side of the world offers insights that those close to the action may not so easily see. These include the possibility that David Cameron sowed the seeds of electoral demise by winning the electoral system referendum of 2011.

This month’s Standpoint magazine features a perceptive essay by Iain Martin, in which he considers David Cameron’s 2015 challenge in terms of inexorable electoral arithmetic. Martin shows forensically why the Conservative Party’s dream of capturing majority government at the 2015 general election will almost certainly remain a fantasy. In short, Cameron is being mugged by reality in the form of Nigel Farage and UKIP.

According to Martin, even if UKIP’s support has peaked – possibly wishful thinking in itself – and Farage’s electoral standing declines before May 2015, it is still likely to cost the Conservatives enough seats to fail to achieve a majority in its own right, let alone keep Ed Miliband and Labour out of government. UKIP “is now regularly polling above 10 per cent of the vote in opinion surveys. Yet it need not score that high in the general election, or win a single seat, to do the Tories damage”, writes Martin. “Even if it sinks back to six per cent or seven per cent, that will constitute in the region of two million votes in a tight election when Cameron needs every vote he can get”.

February’s Wythenshawe and Sale East by-election highlights the Conservatives’ dilemma. While the Tories running third to Labour and UKIP drew much comment, the centre-right vote was hopelessly, pointlessly split, with little impact on Labour’s support. Come May 2015, Cameron and the Tory campaign machine face a serious UKIP challenge that may not win Farage many (indeed any) seats, but may still split the right-of-centre constituency vote to the point that Miliband comes through the middle in marginal after marginal to sneak his way into Downing Street.

If, on 8 May 2015, Cameron finds the removalists at Number 10’s door he may blame the dysfunctional coalition with the Liberal Democrats. He may blame the right-of-centre’s confusion over Europe, of which UKIP is just the most potent manifestation. He may even blame his own political and party management since 2010.

It’s a reasonable bet, however, that should he be defeated the Prime Minister won’t blame the first-past-the-post (FPTP) electoral system for his demise. Yet, when all is said and done, the Conservatives’ problems with UKIP are first and foremost a product of FPTP, because Farage has exploited it very effectively. As its by-election performances since 2010 illustrate, being able routinely to deprive the Conservatives of constituency majorities makes UKIP a legitimate party of protest, if not a potential party of government.

If, however, Britain had an Alternative Vote (AV) electoral system, similar to Australia’s, the political equation for Cameron would have been much different. Under AV, provided that the Conservatives could secure first or second place in as many constituency contests as possible, it could leak “primary” votes to UKIP and other parties, but be reasonably confident that most of these would return to the party for a favourable final result.

To be sure, Labour and the Liberal Democrats would stand to benefit under AV in terms of the centre-left vote. They wouldn’t have embraced it if they didn’t and, indeed, under AV some FPTP Tory blue seats would turn red or yellow. But in 2015 at least, especially given the fractured party system in England and Wales, the Conservatives would be much more likely to defend their heartland and, with exhausting UKIP votes favouring them, win more seats from Labour and the Lib Dems than they would lose.

If AV were operating next year, therefore, it’s very likely that the next Parliament would resemble the two-party template that mostly dominated British electoral politics from 1945 to 1981, with the Conservatives well-placed to form majority government. Given that overall political and economic trends are starting to lean the Conservatives’ way, an AV election also would have given Cameron added confidence and less distraction going into the last twelve months of this term.

But this is not to be, because first-past-the-post prevailed in May 2011. Alone of the major parties, the Conservatives threw their weight behind FPTP and the British public, sticking with the devil they know, supported FPTP overwhelmingly. At the time Cameron basked in a major moral and political victory over his Lib Dem coalition partners and Nick Clegg: only subsequently did the rise and rise of Farage and UKIP make Cameron’s referendum victory very pyrrhic indeed.

In May 2011 Cameron and his political advisers, including George Osborne, feared a permanent centre-left threat majority under AV. But they underestimated the increasing threat of catastrophic splits in the right-of-centre vote at constituency level, apparently forgetting that parliamentary majorities are formed from seats in hand, not overall party vote shares. As Iain Martin highlights in Standpoint, the Conservatives now are in danger of reaping the electoral whirlwind, even if UKIP support wanes over the next year.

Instead of having Nigel Farage breathing relentlessly down his neck, had David Cameron peered more effectively into his crystal ball before the electoral system referendum, he might have seen that AV could well have been the Conservative Party’s electoral salvation in 2015 and beyond. AV would have concentrated the fractious centre-right vote by minimising the impact of UKIP’s incursion into the Tory-leaning constituency vote. It’s how the Liberal party in Australia has prevailed over its left-of-centre opponents again and again.

So if Cameron loses the next general election because of UKIP pinching vital constituency votes, it wouldn’t be far-fetched to say that his fate was sealed on 7 May 2011 when the AV referendum went down. It would be fascinating to know what Cameron’s Australian political guru, Lynton Crosby, who has directed many highly successful election campaigns under Australia’s AV system, thinks about Dave’s judgment in spurning what may otherwise have been his electoral salvation.